This invention relates generally to apparatus and processes for treating an agricultural product and in particular to an apparatus and process for carbonizing an agricultural product having a high silica content.
Of the few agricultural products having a high silica content, rice hulls and the rice plant itselt represent a major disposal problem where uncontrolled burning of agricultural waste is prohibited by various environmental laws.
By controlling the burning of the rice hull and the rice plant to remove volatile constituents and organic matter leaving only the carbon constituents attached to the skeletal silica in the material, a valuable commercial product is obtained which can be used in other chemical processes.
In prior art processes and apparatus, burning temperatures were controlled to be below the temperature which would cause the skeletal structure of the plant material to fuse but high enough to cause the volatile constituents and organic matter to be removed. The process was performed in a combustion zone in which hot gases and combustion air were swirled about a vertical axis while the hull material was continuously provided to the combustion zone. In the prior art process, the processed hulls would fall, pulled by gravity, through the combustion zone and be removed at the lower portion of the zone. In such an apparatus, the particles would not necessarily fall through the combustion zone at the same velocity because of the variation in particle weight and aerodynamic shape or each particle. Some particles would remain in the combustion zone too long causing the carbon constituent to become oxidized while the heavier and more streamlined particles would pass too quickly through the zone and not be completely processed.
In addition, some of the incompletely processed particles would continue to burn after leaving the combustion zone causing uncontrolled oxidation of the carbon contained in the particles resulting in an inferior product.
Such a process would result in a non-uniform product, especially where the rice plant parts are processed along with the rice hulls.